Wholly aromatic polyester resins long have been known. For instance, 4-hydroxybenzoic acid homopolymer and copolymers have been provided in the past and are commercially available. Those wholly aromatic polyesters normally encountered in the prior art have tended to be somewhat intractable in nature and to present substantial difficulties if one attempts to melt process the same while employing conventional melt processing procedures. Such polymers commonly are crystalline in nature, relatively high melting or possess a decomposition temperature which is below the melting point, and when molten frequently exhibit an isotropic melt phase. Molding techniques such as compression molding or sintering may be utilized with such materials; however, injection molding, melt spinning, etc., commonly have not been viable alternatives or when attempted commonly have been accomplished with difficulty.
Representative publications which discuss wholly aromatic polyesters include: (a) Polyesters of Hydroxybenzoic Acids, by Russell Gilkey and John R. Caldewell, J. of Applied Polymer Sci., Vol. II, Pages 198 to 202 (1959), (b) Polyarylates (Polyesters From Aromatic Dicarboxylic Acids and Bisphenols), by G. Bier, Polymer, Vol. 15, Pages 527 to 535 (August 1974), (c) Aromatic Polyester Plastics, by S. G. Cottis, Modern Plastics, Pages 62 to 63 (July 1975); and (d) Poly(p-Oxybenzoyl Systems): Homopolymer for Coatings: Copolymers for Compression and Injection Molding, by Roger S. Storm and Steven G. Cottis, Coatings Plast. Preprint, Vol. 34, No. 1, Pages 194 to 197 (April 1974). See also, U.S. Pat. Nos. 3,039,994; 3,169,121; 3,321,437; 3,553,167; 3,637,595; 3,651,014; 3,723,388; 3,759,870; 3,767,621; 3,778,410; 3,787,370; 3,790,528; 3,829,406; 3,890,256; and 3,975,487.
Also, it more recently has been disclosed that certain polyesters may be formed which exhibit melt anisotropy. See for instance, (a) Polyester X7G-A Self Reinforced Thermoplastic, by W. J. Jackson Jr., H. F. Kuhfuss, and T. F. Gray, Jr., 30th Anniversary Technical Conference, 1975 Reinforced Plastics/Composites Institute. The Society of the Plastics Industry, Inc., Section 17-D, Pages 1 to 4, (b) Belgian Pat. Nos. 838,935 and 828,936, (c) Dutch Pat. No. 7505551, (d) West German Pat. Nos. 2520819, 2520820, 27222120, 2834535, 2834536 and 2834537, (e) Japanese Pat. Nos. 43-223; 2132-116; and 3021-293, (f) U.S. Pat. Nos. 3,991,013;; 3,991,014; 4,057,597; 4,066,620; 4,067,852; 4,075,262; 4,083,829; 4,118,372; 4,130,545; 4,130,702; and 4,156,070; and (g) U.K. application No. 2,002,404. See also commonly assigned U.S. Ser. Nos., 877,917, filed Feb. 15, 1978; (now U.S. Pat. No. 4,184,996) 10,392, filed Feb. 8, 1979, and 10,393, filed Feb. 8, 1979.
Additionally, in my commonly assigned U.S. Ser. No. 834,993, filed Oct. 20, 1977, (now U.S. Pat. No. 4,161,470) is claimed of polyester of 6-hydroxy-2-napththoic acid and para-hydroxy benzoic acid, and in my commonly assigned U.S. Ser. No. 32,086, filed Apr. 23, 1979 is claimed a polyester of 6-hydroxy-2-naphthoic acid, para-hydroxy benzoic acid, aromatic diol, and aromatic acid. Each of these polyesters exhibits an anisotropic melt phase and is capable of readily undergoing melt processing.